This invention relates to composite photography, and more particularly to an improved process for use in motion picture travelling matte photography. It is particularly suitable for the compositing of images incorporating as foreground subjects finely detailed models of aircraft, space ships or the like which have metallic or glossy paint surfaces exhibiting specular optical reflectance and/or which include minute elements such as thin wires, struts, wings or antennae.
In motion picture production, it is sometimes impractical or impossible to place actors in specific environments to be depicted. To resolve this problem, various techniques have been evolved over the years to composite such scenes from separately filmed "elements." Initially, in early films such as Georges Melies' "Trip to the Moon" (1902) animation was resorted to. Thereafter, techniques were utilized such as the "held/take" process, in which a scene was shot with predetermined areas of the successive frames blocked out in order to preclude exposure thereof. The unexposed portions of the successive frames were thereafter exposed to the desired foreground subjects with the background areas blocked off with an opaque matte to protect the previously recorded latent images thereon. Essentially the same process is used to incorporate a painting which depicts the distant, dangerous, or totally imaginary scene against which the actors are to appear; this is known as matte painting.
In order to depict actors or other foreground subjects moving in front of the desired background scenes, various techniques were developed. One early approach involved the so-called "carousel" in which motion effects were simulated, for example, by photographing actors on dummy horses or in automobiles in front of a cylindrical, painted backdrop revolving through the frame behind the actors. This technique evolved into rear projection/front projection filming operations in which a separately filmed background scene was projected onto a screen behind the foreground subject and re-photographed simultaneously therewith to produce a composite image.
The use of such operations, however, necessitates synchronizing the rear projection system and the front projection camera, as well as accurate balancing of both the illumination across the projected image of the background scene and the illumination and color balance of the foreground subject, relative to the background scene. Moreover, such techniques are inherently expensive, requiring the prior filming and independent processing of the background scene and the additional expensive studio time for filming the foreground subject in conjunction with the background plate. There is usually a discernable loss of image quality in the rephotographed projected image when compared to the original photography of the foreground action.
To retain both image quality and the flexibility inherent in optical compositing, while insuring the freedom of movement basic to the front projection technique, it became necessary to create mattes which would change from frame to frame, or "travel." Such "travelling mattes" were initially produced manually or mechanically; in order, however, to meet the ever-increasing demand for fidelity, a wide variety of photographic techniques for producing travelling mattes have subsequently been developed. Such generally utilize either the so-called "single-film" or "multi-film" approaches.
Several single-film and multi-film systems of travelling matte cinematography have been described in the patent literature. See, for example, U.S. Pat. Nos. 1,673,019; 1,863,827; 1,955,993; 2,013,886; 2,028,863; 2,232,144; 2,277,141; 2,297,598; 2,461,127; 2,609,294; 2,651,233; 2,693,126; 2,740,712; 3,037,422; 3,095,304; 3,149,969; 3,158,477; 3,260,563; and 3,902,798. The preceding and like travelling-matte systems have also been reviewed in the technical literature. See, for example, "Travelling-Matte Photography and the Blue Screen System," Beyer, Journal of the Society of Motion Picture and Television Engineers, March 1965, Vol. 74, No. 3, pp. 217-236; "The Technique of Special Effects Cinematography," Fielding, 1968, pp. 218-253; and "Talking Technically," David Samuelson, American Cinematographer, May 1982, page 434, and June 1982, page 588.
Early single-film matte processes relied upon contrast alone, the foreground action being filmed against a jet black backing and the resulting image being printed through several generations of high contrast film stock until a matte was produced. The results obtained by this technique were generally quite poor, due to the inevitable distortion produced by the multiple reversals.
Subsequently, with the advent of subtractive color film, a single film technique was developed which relied upon the dedication of one of the three emulsion layers of the color negative film to the matte. While all three emulsion layers have been utilized from time to time for matte formation, the blue layer has always been preferred. Consequently, the dominant travelling matte process extant in the industry today is the "blue screen" process.
While there are numerous variations of the blue screen process, each generally involves exposure of a color negative film to a foreground subject in front of a blue backing. The backing may, for example, be a front lit painted backing, a projection screen which is front lit by reflection from a blue light source, or a rear lit translucent blue transmission screen. The color negative image thus formed is utilized, dependent upon the particular technique employed, to produce sets of black and white separation negatives and matte images. The mattes are thereafter used to facilitate compositing of the foreground subject with the image of a separate background scene.
Prior single-film matte processes have, however, been subject to a number of disadvantages. Thus, rapidly moving objects whose images streak, as well as finely detailed subjects such as hair, or glass, are difficult to reproduce without "fringing," i.e., producing either a truncation of the subject or a black border or "matte line" adjacent to it. In the case of rapidly moving objects, for example, their partially exposed edges either "drop in" or "drop out" of the matte in sequential frames, thereby producing the fringing effect. Moreover, there can be nothing in the foreground subject which is pure blue in color, since it would be matted with the blue screen and permit the background scene to show through the "hole" during compositing. While techniques have been developed to resolve these problems (see, for example, Vlahos U.S. Pat. No. 3,158,477) such have been uneconomical in both time and materials.
Various multi-film systems have also been developed for the formation of travelling mattes. Such typically require the huge, complex "Technicolor" camera, and employ the simultaneous exposure through a beam splitter of a color negative film and a further film sensitive to some narrow portion of the spectrum. The matte image is thereby formed on the latter film, thus eliminating the necessity to produce separation negatives, and obviating the loss of any portion of the spectrum for matte formation. Such techniques (see, for example, Vlahos U.S. Pat. No. 3,095,304) may be utilized in the formation of travelling mattes of objects which move or which have fine details (e.g., hair) without fringing.
In recent years the filming of elaborate science fiction films has necessitated the compositing of numerous, finely detailed models defining foreground subjects such as space ships and the like, under conditions designed to simulate high speed, "real" relative motion therebetween. It has become necessary to produce many overlapping images and to record "streak," that blurring of a moving subject when photographed which allows the human eye to perceive and interpret the movement as real. In producing such special effects, it is desirable to employ the largest possible film format in order to reduce the image degradation resulting from the numerous reversals required to produce the final composite images. Moreover, the cameras necessary to photograph the miniature models required for such purposes must themselves be miniature in order to maneuver about their nodal points in close proximity to the models.
In view of the preceding requirements, it has not been feasible to utilize the multi-film system of travelling matte cinematography in the production of recent special effects films. Since available multi-film systems require both the use of a relatively large and complex camera and a relatively small size film format, they are simply inadequate.
For the production of the special effects in the motion picture "Star Wars", special motion control systems were developed to permit miniature cameras to make numerous passes relative to multiple miniature models to be photographed in perfect registration and at variable exposure rates. Employing such a motion control system, it is possible to obtain substantially the same quality travelling mattes produced by the use of multi-film matting techniques, merely by filming consecutive passes relative to the foreground subject (the miniature model or models)--the "matte" pass and the "subject" pass being photographed separately and sequentially on the same film load. By exposing the models on the matte pass in front of a back-lighted blue screen in conjunction with a blue filter at the camera, very pure monochromatic blue matte images are produced.
A major problem with any travelling matte system which utilizes an illuminated screen behind a foreground subject to produce a matte is, however, that the radiation transmitted from the screen, whether it be infrared, ultraviolet or within the visible spectrum, is reflected from any glossy or specular metallic surface on the foreground subject. In fact, it was found in the filming of "Star Wars" that the problem of reflected light ("blue spill") is exacerbated whenever a wide angle lens is utilized, since the model or other subject to be photographed must then be relatively close to the blue screen to permit sufficient blue screen area in the frame surrounding the subject. Various techniques have been developed to improve matte formation, notwithstanding blue spill; these include the exposure and matting of various back-up passes of the models to be photographed and the formation of a so-called "garbage matte" to mask the light stands and assorted paraphernalia illuminated by the untoward blue spill. Apart from the use of such auxiliary techniques, however, the minute reflective elements, e.g., wires, thin wings, struts, etc., of the finely detailed models photographed are apt to be "wrapped" by the transmitted light, and "drop out" of the resulting matte, resulting in holes or separations therein.
It is, accordingly, among the objects of the present invention to provide an improved blue screen process for travelling matte cinematography which overcomes the disadvantages of conventional blue screen processing of images of highly reflective and/or finely detailed foreground subjects, without necessitating any additional matting steps or the like. A further object is to provide such a process which is particularly useful in special effects cinematography of miniature models or other foreground subjects which may have to be photographed under conditions designed to simulate rapid relative movement therebetween. These and other objects and advantages of the present process will be apparent from the following description of preferred embodiments thereof taken in connection with the accompanying drawing.